Under the auspices of the proposed Center for Prevention Methodology, prevention scientists and methodologists will collaborate to identify important methodological issues in prevention research, to address the issues in a scientifically rigorous yet practical way, to apply the new techniques in empirical prevention data, and to place the solutions in the hands of researchers. The overall theme of the proposed center is Bringing Prevention Science and Statistics Together to Enhance Drug Abuse Prevention Research Methodology. The components making up the proposed center are conceptually distinct yet tightly integrated logistically and thematically. In addition to Components I and 11, two cores which will provide infrastructure and centralized resources, the center includes four scientific components, each of which will develop new statistical methodology directly addressing important methodological issues in prevention. Component III will expand Latent Transition Analysis, a procedure for modeling stage sequential processes in longitudinal prevention data. Component IV will develop statistical methods for analyzing prevention data with complex longitudinal structures. Component V will develop procedures to draw valid inference from prevention studies involving time varying treatments. Component VI will develop better procedures for dealing with missing data in prevention studies.